Erickson Dimas-Martinez: the Arkansas supreme court overturned his murder conviction after a juror used Twitter despite the judge’s instruction not to post on the internet. Photograph: AP

The supreme court in the US state of Arkansas has thrown out a death row inmate's murder conviction because a juror tweeted during court proceedings.

Erickson Dimas-Martinez's attorneys appealed against his 2010 murder conviction because a juror used Twitter despite the judge's instruction not to post on the internet or communicate with anyone about the case. The lawyers complained that another juror slept.

In one tweet, juror Randy Franco wrote: "Choices to be made. Hearts to be broken … We each define the great line." Less than an hour before the jury announced its verdict he tweeted: "It's over."

Other tweets by Franco made passing references to the trial, with posts such as "The coffee sucks here" and "Court. Day 5. here we go again".

The court said Franco, known as Juror 2 in court documents, violated general instructions to not discuss the case. Before opening arguments, the judge said: "Just remember, never discuss this case over your cell phone … and don't Twitter anybody about this case."

Franco didn't immediately return a message left on Thursday but has defended his tweets in the past. "None of my texts indicated anything about the trial," he told the Arkansas Democrat-Gazette last year. "I hadn't made up my mind."

Associate Justice Donald Corbin wrote in the supreme court verdict: "Because of the very nature of Twitter as an … online social media site, Juror 2's tweets about the trial were very much public discussions. Even if such discussions were one-sided it is in no way appropriate for a juror to state musings, thoughts or other information about a case in such a public fashion."

The judges used the case to point out that a wide array of juror misconduct could come into play when jurors had unrestricted access to their mobile phones during a trial.

"Most mobile phones now allow instant access to a myriad of information. Not only can jurors access Facebook, Twitter, or other social media sites but they can also access news sites that might have information about a case," Corbin wrote.

He asked a panel to consider whether to limit jurors' access to mobile phones during trials.

Dimas-Martinez, now 26, was sent to death row for robbing and shooting a teenager after a party in north-west Arkansas in 2006. Prosecutors said he held 17-year-old Derrick Jefferson at gunpoint and demanded money, then shot him.